Modulable lamp construction



Sept. 3, 1957 E. LEMMERS Erm.

MODULABLE LAMP CONSTRUCTION Filed Oct. 29, 1954 Ilv mh. ey Sew n PmV P mmm; HL ew/ nmmvw Tfwvn//f EAWT f nited States Patent z,scs,ss4

Monument: Lam CONSTRUCTION Eugene Lemmers, Cleveland Heights, and Andrew Kovach, Euclid, Ohio, assignors to General Electric Company, a corporation of New York v Application Gctober 29, 1954, Serial No. 465,466

Claims. (Cl. 313-193) This invention relates in general to modulable electric discharge lamps or devices useful for translating an electric signal into a variation in intensity of light or other radiation. Such lamps approximate point sources and are particularly useful for achieving fine resolution in the transmission of printed material or pictures by electrical means as in facsimile transmission. The invention relates more particularly to lamps of this type wherein the source of radiation is an end-on viewed positive column.

In Patent 2,445,678 of Eugene Lemmers, entitled Electric Discharge Device, there is described a modulable lamp wherein the light source is a positive column viewed end-on through an apertured anode. The intensity or brilliance of radiation from the discharge can be modulated by vvarying the discharge current. In the preferred construction described, an auxiliary apertured anode or control electrode, is positionedalong the path of the positive column intermediate the main anode and the cathode. By maintaining a potential difference between the cathode and this auxiliary anode, a part of the discharge is diverted from the main discharge with the result that the end-on intensity of radiation from the main discharge varies in greater proportion than the total discharge current. Y

In a modulable lamp wherein the useful light or radiation output is that produced by the positive column, it is desirable to eliminate or reduce as much as possible the effect of the light produced by the negative glow about the cathode. When the light produced by the negative glow is allowed to add to that produced by the positive column, since the eect of the signal applied to the lamp is less in the negative glow than in the positive column, the end result is a reduction in the effective modulation of the light output by the signal.

Accordingly, one object of the invention is to provide an improved modulable lamp of the positive column type wherein the effect of the light'produced by the negative glow about the cathode is eliminated or substantiallj reduced.

Another object is to provide a modulable'lamp with an improved cathode construction having desirable features and characteristics for the intended use of the lamp.

Yet another object of the invention is to provide an improved modulable lamp of simple and ruggedconstruction facilitating manufacture and giving reliability of operation.

According toa feature of the invention, there is provided a cold cathodeinY the form of an electron-emissive member located in a plane substantially perpendicular to the axis of the positive column to be energized thereby Y and apertured along the axis of the positive column. As a result, the light from the negative Vglow which bathes the plate during operation is substantially eliminated from the optical system which views the positive column end-on. In a preferred embodiment, the cathode comprises plural parallel spaced plates, each apertured along the axis of the positive column. According to..another .feature of the invention, the cathode is mounted within a hollow Cil insulator body which is apertured along the axis of th positive column. The anodes are mounted on the exterior of the insulator body about or beyond the aperture and the leads for supporting and conducting current tothe anodes are passed through holes or channels through the walls of the insulator. The insulator thus serves not only to provide mechanical support for the electrodes and optical masking of the discharge region, but serves also to insulate the lead wires to the anodes from the cathode and the ionized region about it. Y Y

F or further objects and advantages and for a better understanding of the features of the inventionQattention is now directed to the following description of embodiments thereof described in conjunction with the accompanying drawings. The features of the invention believed to be novel will be more particularly pointed out in the appended claims.

In the drawings:

Fig. 1 is a perspective view of a modulable lamp of the positive column type embodying the invention;

Fig. 2 is a fragmentary perspective view of a similar lamp having two positive column discharges and likewise embodying the invention.

Referring to Fig. l, there is shown a modulable lamp of the positive column type which resembles in size and external configuration a small glass radio receiving tube. The envelope 1 (shown partly broken away) is a cylindrical glass bulb with the usual stem and ilare closure 2 at one end, including a press 3 through which are sealed lead wires 4 7 whose inner projections within the bulb serve also as support wires for and conductors to the various elements therein. The outer projections of the lead wires are soldered into the pins 8 of an octal-type base 9 cemented in the usual fashion to the sealed end of the envelope. Y

Positioned within the envelope immediately above the press 3 is an insulator body 11 having a generally cylindrical hollow interior with its axis coinciding with the longitudinal axis of the envelope. The insulator body, as illustrated herein, is made up of two parts, one part being a circular disk 12 and the other a hollow cylindrical shell 13 (shown broken away along a diametral plane for greater clarity). The disk and the shell have an outside diameter just slightly under the inside diameter of the glass envelope, so that the insulator body fits within the envelope with small clearance between the enveloperand insulator walls. Both parts of the insulator body are made of a suitable material, lava, for instance, which is readily machined. For mass production, a ceramic which can be molded to shape and then baked hard, for instance those sold commercially under the names steatite or sillimanite, is preferred. The disk 12 is provided with a raised circular step 14 whose edge forms a flange which lits against the inside lower edge of the side wall of shell 13 to assure accurate seating of the two parts. The space within the insulator body bounded by the lower or inside surface ofV the circular Vend wall of shell 13 and the surface of step 14 forms a cathode cavity which is electrically insulated and optically masked from the remainder of the envelope interior and particularly the portion thereof aboveor in front of the upper surface of shell 13.

Theshell and the diskare drilled through at 15, 16 to provide aligned holes orA channels in both parts extending through the cylindrical side wals of the shell. Lead wires 4, 7 or extensions welded thereto are extended from the press through these channels to the electrode elements in the space above the insulator body and ,provide electrical connections thereto. The leadsor their welded extensions, are preferablyrbent fairly sharply at the points of entrance into and emergence from the'holes through the insulator body whereby to lock disk 12 and shell 13 axial- E ly together.` Additional support wires 17 sealed into the press may be extended through other channels in the insulator body to provide additional suport. The circular end wall of the shell is provided with a central circular aperture 18 which is chamfered at 19 on the outer sur- Y insulating disk 12. Whereas three disks have been shown here, it will be appreciated that a greater or lesser number may be used in accordance with the current rating of the lamp. The disks lare conductive and have electron-emissive services; they may consist Yof nickel coated with a mixture of barium and strontium oxides. The spacing between two adjacent disks, for instance 22, 23 or 23, 24, is much less than the mean-free pathlof the electrons in the ionizableV medium with which the lamp is lled; for instance, it may be 1,64 to 1A; inch. This produces a hollow cathode eiiect, as a result of which electron-emission increases more linearly with applied voltage, vbecause electrons rebound from the cathode Walls and knock out more electronsinthe process. The cathode disksare maintained in spaced alignment by the welded wire straps 25 and the cathode connection is made through lead wire 6 which is Welded to the lowermost disk 22 and extends through the press to one of the base pins 8. Y

All the cathode disks have a central holeat 26 in Yaxial alignment with aperture 18 in the circular end wall of ,the insulator shell 13. The lhole 26 is substantially larger than the aperture 18 in order to prevent the cathode glow which bathes the surfaces of the cathode disks from being visible through the aperture in the insulator shell. It will be lobserved that the cathode disks 22-24 are positioned in a plane substantially normal to theV axis of the positive column discharge extending through aperture 18. Thus, the invention provides for the region of cathode glow, namelyA the surfaces of the cathode disks, to extend at right angles to the optical axis yof the lamp. This feature, in conjunction with the feature of the holes 26 in the yaperture 18 in the insulator shell and axially aligned therewith. The anode shell may be formed by bending a strip of sheet metal into a loop land Welding along a medial seam with the ends turned out to form a tab 29.

the seamtab andV provides a'connectio'n to a suitable one of the pins 8 in thebase. The auxiliary anode or control electrode 28 consists of a flanged metal' sleeve or eyelet, of nickel-plated iron for instance, which is fitted into It Vis supportedV in place by the lead wire 4 which is welded toV Vpositive columns operating Vfrom a single cathode.

aperture 18, the iiange ofthe eyelet resting in the cham- `fered outer portion 19 of theaperture'.V The-cylindrical portion of the eyelet extends substantially thelength of vaperture 18. The control electrode or eyelet is held in placeY by friction and Yalso byl'ead wire 7 Vperipherally welded thereto and through which it is connected to one of pins 8.A YThe sizeof the eyelet hole of control electrode V28'determines substantially Vthe eiective area pf the light Ysource and for this reason it is made as small as possible 4 consistent with the quantity of light required to be obtained from the lamp.

The lamp is evacuated and filled with a suitable ionizable mediumconsisting of a starting gas at a low pressure and a small quantity of mercury. The evacuation 'and filling is done vthrough exhaust tube 31 which is then sealed by tipping off at 32. A suitable starting gas consists of a mixture of neon with a few percent of argon at a low pressure. The mercury is indicated by the supe ply droplet 33 inside the envelope, and is preferably in excess of the amount required toY saturate the filling at the operating temperature of the lamp. Across the ends of leads 5, 6 is connected a resistance heater 34, such as a coiled-coil of'fine tungsten wire. The current through this heater may be thermostatically controlled to maintain a constant temperature within envelope 1 despite wide variations in 'ambient temperature. A getter strip 35 -consisting of a barium-containing metal may be provided to clean up any residual gases during the evacuation process.

In operation, the discharge current in the lamp is proportional to the signal intensity applied between cathode 21 and the two anodes, namely, main anode 27 and control |anode 28. The intensity of the endwise radiation from the'discharge, that is the intensity viewed along the longitudinal axis of the lamp looking into the aperture through control electrode 28, depends on the discharge current :and also on the axial length or depth of the positive column. In the absence of control electrode 28, the discharge would always extend in full strength Vclear to the main 'anode 27; in :other words, its length would be Y constant land its intensity would vary in sole dependence on the discharge current. The lamp may be operated in a suitable amplifier with its cathode and main anode connected in series in the plate circuit of an electronic power amplifier tube. The control electrode ofY the lamp may be connected to` the main lanode of the lamp through a resistance which will maintain'the control electrode at a lower'positive potential relative to the cathode than the main anode 27. With such an arrangement, part of the discharge in the lamp goes to the control electrode, thereby shortening the axial length of the discharge and diminishing its end-on intensity of radiation. The degree to which this takes place depends on the magnitude of the resistance connecting the control electrode to the main anode, aswell as on the position of the control electrode and itsarea per unit of length. The effect is proportionally greater for'low currents, since the smaller the current flow, the greater the proportion of it that can be accom-V modated by the path via the control electrode, which gives rise to a lower intensity of radiation than yan equal current via the main anode 27. Thus, the provision of the auxiliaryjanode or control electrode with Yits resistive connection to the main lanode makes the end-on intensity of radiation toward the receiving optical system vary in `a greater ratio than thedischarge current and this ratio can be adjusted by adjusting the coupling resistance.

Fig. 2 illustrates lanother embodiment of the invention` applied to a double positive column modulable lamp following the teachings of copending application No. 465,465 of Eugene Lemmers, led ofeven dateY herewith, entitled Modulable Discharge Lampf. and `assigned to the same assignee `as the Vpresent invention; This lamp provides two BY modulating the 'two positive columns in opposite phase' relation, the total discharge'. current from the Ycathode remains substantially constant, sothat the Wattage loss in the lampremains constant irrespectively of the signal intensity. This assures 'a constant mercury pressure within the lamp, Vthereby providing improved stability'in the relation between generated radiation Iand'discharg'e current or signal. y .Y

Y Referring to Fig. 2, the lamp comprises, 'asin the embodiment of Fig. 1, a generally cylindrical glassenvelope 1 with the usual stem and flare closure and a press (not accessi shownlthrough which are sealed leadwires 4--7 and a of'additional lead wires 4',7'. The insulator shell 13 is here provided with an additional aperture 18 located to`the`side of central aperture 18. Cathode 21 consists of a pair of parallel disks 22, 23 coated with electronemitting material, such as barium and strontium oxides. The disks, in addition to the central holes at 26, have lateral openings `orcutouts at Z6 in axialalignment with side aperture 18' in the circular end wall of the insulator shell.

Central aperture 18 Vthrough the insulator shell laccommodates `one positive column path whichis theone which will normally be used with the optical system cooperating with the lamp. Side aperture 18' 'accommodates the other positive column discharge path Whose main function is tostabilize the wattage dissipation at the cathode but which may also be used optically if desired, for instance, in producing a negative image of the transmission received by the lamp. The electrode elements for the Iside discharge path are similar to those for the central discharge path, namely, a main anode 27 in the form of a cylinder and a control electrode 28 in the form of 'a hanged eyelet tted within aperture 18 and with the ange resting in the upper chamfered side of the aperture. Side main anode 27 and side control electrode 28 are connected through lead wires 4', 7 to suitable ones of pins 8 in base 9.

The modulable lamp of Fig. 2 operates in ys-imilar fashion to that of Fig. l as regards the modulation of the intensity of radiation in each positive column. In addition, by supplyinga signal of opposite phase to the anodes of each discharge path, the cathode current, and accordingly the Wattage dissipation of the lamp, is maintained constant so that the mercury pressure remains constant irrespective of the signal intensity. The provision of the lateral cutouts at 26T Vin the cathode disks corresponds in purpose-to the holes 'at 26 and assures that the radiation from the negative glow about the `cathode is substantially eliminated from the light received by viewing the positive ycolumns end-on.

The-insulator shell 13 is provided with a projecting portion 36 extending substantially to the end Wall of the glass envelope. This portion is generally of double concave form when Viewed in section transverse to the longitudinal axis ofthe lamp. It serves as a light partition'to render the two positive columns optically independent of eachother and at the same time assists in insulating the anodes of the two columns from each other.

For the convenience of those desiring to practice the invention, essential illustrative particularsof a discharge device, such as shown in Fig. 2, are here given. The envelope 3. may be about l inch in internal diameter and 2%.V inches long, with a substantially at frontl end and with the stem and press extending forward into the interior of the bulb about 1% inches. The insulator body 3rnay be about S/s inch in axial length and with the cathode cavity therein approximately 3A inch in diameter and 1A inch in axiallength. The'comparative dimensions of the electrode elements may readily be seen in the drawing. The drawings illustrate that the thickness of the cathode plates is insignificant relative to the axial length of the discharge pathand also that the distance from the anode to the plane ofthe nearest cathode plate is at least several times the mean-free path in the discharge medium. The illustrated construction thus provides suicient anode-to-'cathode spacing to accommodate in the discharge path a positive column of'substantial intensity. Such a lamp with a filling of a mixture of neon Vand 0.8 percent argon at 45 millimeters pressure, and with an excess of mercury, operates with Va voltage drop which remains substantially constant at about 90 volts. The current in each discharge path is variable between-2 and 32 milliamperes: at zero signal, one path draws 32 and the other draws 2 milliamperesrat middle signal value; each pathdraws 1:7"millia`mperes:

While-certain specinc embodiments of the-invention have been shown and described,Y it is to-be understood that these have been provided by way of illustration and not in order to limit the inventions thereto. Obviously, invention admits of many modincations in the dimensions and specific details of the described structures. The appended claims are therefore intended to cover any modiiications coming within the true spirit and scope of the invention.

What We claim as new andV desire to secure by Letters Patent of the United States is:

l. A gaseous electric discharge device operable With a positive column comprising a sealed envelope containing an ionizable medium, a cathode, an insulating body partitioning ol a portion of said envelope from the region about said cathode, an aperture'through said insulating body, said cathode comprising a-v thin electron-emissive member disposed in a plane substantially normal to the axis of a discharge path therefrom through said aperture and having a hole therethrough aligned with said axis and substantially larger than said aperture, said member being of insignificant thickness relative to the axial length of the discharge path, and an anode located beyond said insulating body in the partitioned-off portion of said envelope, the distance from the anode to the plane of the cathode through said aperture being at least several times the mean-free path in said medium and sutlicient to accommodate in the discharge path a positive column of substantial intensity. Y

2. A gaseous electric discharge device operable with a positive column comprising a sealed envelope containing an ionizable medium, a cathode, an insulating body partitioning oit a portion of said envelope from the region about said cathode, an apertureV through said insulating body, said cathode comprising plural spaced thin plates disposed in planes substantially normal to the axis of a discharge path therefrom through said aperture and having holes therethrough aligned with said axis and substantially larger than said aperture, said plates being of insignificant thickness relative to theaxial length of the discharge path, and an anode located beyond said insulating body in the partitioned-o portion of said envelope, the distance from the anode to the planeof the nearest cathode plate through said aperture being at least several times the mean-free path in saidY medium and sufcient` to accommodate in the discharge path a positive column of substantial intensity'.

3. A gaseous electric discharge device operable with a positive column comprising a sealed envelope containing an ionizable medium including an inert starting gas and mercury, a cathode, an insulating body partitioning otr` a portion of said envelope from the region about said cathode, ank aperture through said insulating body, said cathode comprising a thin plate disposed in a plane substantially normal to theaxis of a discharge path therefrom through said aperture and having a hole therethrough aligned with said axis and substantially larger than said aperture, said plate being of insignificant thickness relative to the axial length of the discharge path, and an anode located beyond said insulating body in the-partitioned-off portion of said envelope and having anopening therethrough aligned with said axis whereby to dene with saidY cathode a positive column discharge path through said aperture viewable end-on`through the opening in said anode, the distance from the anode tothe plane of said cathode plate through said aperture being at least several times the mean-free path in said medium and sufficient to accommodate in the discharge path a positive column of substantial intensity.

4. A gaseous electric discharge device operable with' a positive column comprising a sealed envelope containing an ionizable medium including an inert startingl gas and mercury, a cathode, an insulating. body partitioning oi la portion of said' envelope fromV thev region. about said cathode, 'an aperture through said insulating body, said cathode comprising a plurality of relatively closely spaced thin parallel plates disposed in planes substantially normal to.V the Yaxis of Va discharge path therefrom through said aperture and having holes therethrough aligned with said axis and substantially larger than said aperture, said plates being of insignificant thickness relative to the axial length of the discharge path, and an anode located beyond said insulating body in the partitioned-off portion of said envelope Vand having an opening therethrough aligned with said axis whereby to define with said cathode a positive column discharge path through said aperture viewable end-on through the opening in said anode, the distance from the anode to the plane of theV fnearest cathode plate being at least several times the mean-free path in said medium and suliicient to accommodate inthe discharge path a positive column of substantial intensity.- .Y

5. A gaseous electric discharge device operable with a positive .column comprising a sealed envelope containing an ionizable medium including an inert starting gas and mercury, a cathode sealed within said envelope, an insulating body partitioning oit a portion of said envelope from the region about said cathode, an aperture through said body having an axis directed toward said cathode, said cathode comprising a plurality of spaced parallel thin plates activated Iwith electron-emitting material and having holes therethrough substantially larger than and aligned with said aperture, said plates being disposed normal'to the axis of said aperture and having a spacing therebetween less than the mean free path of electrons in said medium, a hollow anode located beyond said insulating body in said partitioned-ott portion and aligned with said aperture and cooperable with said cathode to deline therewith a positive column discharge path viewable end-on through said anode, whereby radiation resulting from negative glow about said cathode is substantially eliminated from the radiation received by viewing said positive column discharge end-on, said plates being of insignificant thickness relative to the axial lengthV of the discharge path and the distance from the anode to Y Y the plane-of the nearest cathode plate being at least sevstantially at right angles to the axis of said lamp and havt ing central holes therethrough, a central aperture in the Y front end wall of said insulating body, the central holes in said cathode Vplates `being substantially larger than said aperture, a hollow cylindrical anode toward the front of said insulating body and encircling said aperture to define with said cathode a positive column'dischar'ge path extending through said aperture, the thickness of said cathode plates being insignificant relative to the axial length of the discharge path, and the distance fromy said anode axially disposed within said envelope, acathode within said cavity comprising a plurality of spaced parallel disks coated. with electron-emitting material, said cathode disks being disposed substantially at right angles to the axis of said lamp and having central holes therethroughya central aperture in the front end wall ofV said insulating body distant from said cathode, a main hollow cylindrical anode infront of said insulating body and disposed about said aperture to deiine with said cathode a positive column discharge path extending through said aperture, an auxiliary hollow anode of generally cylindrical form lining the walls of said aperture, lead wires sealed through the rear end wall of said envelope, Vand individual channels through said insulating body with lead wires` projecting therethrough to said anodes. Y Y, t

8. A modulable gaseous electric discharge device comp rising as e'aled generally cylindrical envelope containing an ionizable medium including an linert starting gasand mercury, a hollow insulating body located within said envelope and comprising a generally cylindrical hollow shell and a disk fitting over the open end thereof, said Y shell and disk together'dening aV generally cylindrical cathode cavity axially disposed within said envelope, a cathode within said cavity comprising a plurality of spaced parallel disks coated with electron-emitting material, said cathode disks being disposed substantially at right angles to the axis of said lamp and having central holes therethrough, a central aperture in the front end wall ofsaid insulating body'distant from said cathode,V a main hollowA cylindrical anode in front of said insulating body and disposed about said aperture to define with said cathode a positive column dischargefpath extending through said aperture, an auxiliary hollow anode of generally cylindrical form lining the walls of said aperture, lead wires sealed through the rear end wall of said envelope, and individual channels through the side walls of said shell and through said disk with lead wires projecting therethrough to said anodes, said lead wires being formed to the plane of the nearest cathode plate being at least t several Atimes theVmean-ree path in said medium and sufiicient to support in the discharge path a positive'column Qi?` substantial intensity, lead wires sealed through the rear endwall ofsaid envelope and at least one channel through said insulating body with one lead wire projecting therethrough to said anode.

7,. A modulable gaseous electric discharge device comprising a sealed generally cylindrical envelope containing an ionizable medium including an inert Vstarting gas and mercury, a hollow insulating body locatedwithin said envelope and dening a generally 'cylindrical cathode'cavityV toV prevent axial displacement of said shell and disk.

- 9. A modulable gaseous electric discharge device comprising a sealed generally cylindrical envelope containing an ionizable medium including an'inert Vstarting gas and mercury, a hollow insulating body located within said envelope and defining a generally cylindrical cathode cavity axially disposed within said envelope, a central and aside aperture in the front end wall of said insulating body, a cathode within said cavity comprising a plurality of spaced parallel disks coated with electron-emitting material, said cathode. disks'being disposed substantially at right angles to the axis of said lamp and having central and side openings therethrough aligned with said central and side apertures respectively, a pair of main hollow cylindrical anodes in front of said insulating body and disposed about said apertures to dene with said cathode a pair of positive column discharge paths extending through respective ones of said apertures anda pair of auxiliary hollow anodes of generally cylindrical form lining the walls of said apertures. Y

Y 10. A modulable gaseous electric discharge device comprising a sealed generally cylindrical envelope containing an ionizable medium including an inert starting gas and mercury, a hollowY insulating body located within said envelope and defining a generally cylindrical cathode cavity axially disposed within said envelope, a central and a sideaperture in the front end wall of said insulatingV body,ra cathode within said cavity comprising a plurality of spaced parallel disks coated with electron-emitting materiahsaid cathode'disks being disposed Ysubstantially at right Vanglesto the axis of said lamp and having cen- Vtral and side openings therethrough aligned with said central and side Yapertures respectively, a pair of main hollow cylindrical anodes in front of said insulating body and disposed about said apertures to dene with said cathode a pair of positive column discharge pathsY extending through respective ones Aof said apertures, a pair of 'auxiliary hollow-.anodes of generally cylindrical form lining the walls of said apertures, lead Wires sealed through the rear end wall of said envelope, individual channels through said insulating body with lead wires projecting therethrough to said anodes, and a projecting portion on the front end wall of said insulating body forming a 5 partition between said main anodes.

References Cited in the file of this patent UNITED STATES PATENTS 1,991,480 williams Feb. 19, 1935 1 y 1o r Clapp Dec. 30, 1947 Lemmers July 20, 1948 Lemmers July 20, 1948 Buckingham et al. Nov. 9, 1948 Bouchard Dec. 28, 1948 Buckingham Aug. 24, 1954 

